HDMI (High-Definition Multimedia Interface) is a compact audio/video interface for transmitting uncompressed digital data. It represents a digital alternative to consumer analog standards, such as Radio Frequency (RF) coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, and VGA. HDMI connects digital audio/video sources—such as set-top boxes, Blu-ray Disc players, personal computers (PCs), video game consoles (such as the PlayStation 3 and Xbox 360), and AV receivers—to compatible digital audio devices, computer monitors, and digital televisions.
HDMI supports, on a single cable, any TV or PC video format, including standard, enhanced, and high-definition video; up to 8 channels of digital audio; and a Consumer Electronics Control (CEC) connection. The CEC allows HDMI devices to control each other when necessary and allows the user to operate multiple devices with one remote control handset. Because HDMI is electrically compatible with the signals used by Digital Visual Interface (DVI), no signal conversion is necessary, nor is there a loss of video quality when a DVI-to-HDMI adapter is used. As an uncompressed connection, HDMI is independent of the various digital television standards used by individual devices, such as ATSC and DVB, as these are encapsulations of compressed MPEG video streams which can be decoded and output as an uncompressed video stream on HDMI.
HDMI products started shipping in the autumn of 2003. A large number of Consumer Electronics (CE) and PC companies have adopted the HDMI specification (HDMI Adopters). In Europe, either DVI-HDCP or HDMI is included in the HD ready in-store labeling specification for TV sets for HDTV, formulated by EICTA with SES Astra in 2005. HDMI began to appear on consumer HDTV camcorders and digital still cameras in 2006.
The Display Data Channel (DDC) is a communication channel based on the I2C bus specification. HDMI specifically requires support for the Enhanced Display Data Channel (E-DDC), which is used by the HDMI source device to read the E-EDID data from the HDMI sink device to learn what audio/video formats it supports. HDMI requires that the E-DDC support I2C standard mode speed (100 kbit's) and allows optional support for fast mode speed (400 kbit/s). HDMI has three separate communication channels, which are the DDC, TMDS, and the optional CEC.
Transition Minimized Differential Signaling (TMDS) on HDMI carries video, audio, and auxiliary data via one of three modes, called the Video Data Period, the Data Island Period, and the Control Period. During the Video Data Period, the pixels of an active video line are transmitted. During the Data Island period (which occurs during the horizontal and vertical blanking intervals), audio and auxiliary data are transmitted within a series of packets. The Control Period occurs between Video and Data Island periods.
Both HDMI and DVI use TMDS to send 10-bit characters that are encoded using 8b/10b encoding for the Video Data Period and 2b/10b encoding for the Control Period. HDMI adds the ability to send audio/auxiliary data using 4b/10b encoding for the Data Island Period. Each Data Island Period is 32 pixels in size and contains a 32-bit Packet Header, which includes 8 bits of BCH ECC parity data for error correction and describes the contents of the packet.
A number of transmitter components are now available that are designed to connect to a receiver component, such as a TV or monitor using the HDMI port that is now commonly provided on TVs and monitors. A game console is one example of a stand alone, battery powered transmitter component that may be connected to a TV or monitor and provide interaction with a game that is displayed on the TV or monitor. Unlike the universal serial bus (USB) that allows for connection of various components to a computer and which provides a power signal that can be used to power a small device, the HMDI does not provide a power signal for use by a transmitter component connected to the HMDI port. The only power signal included in the HMDI port is a 5 volts signal that is intended to allow the transmitter component to provide power to an identification ROM (read only memory) on the receiver component to allow the transmitter component to determine the capabilities of the receiver by reading the ID ROM.